I'll add my stock answer here...
OnDemand & Streaming services on the TiVo (NOT the V6) have two issues:
1: The box is quite old and runs old hardware, it can struggle with the streaming apps (iPlayer, Netflix, YouTube) especially and this is one (of a few) reason why the additional apps are only available on the V6. There isn't any way of sugar-coating this, I'm afraid. @jb66 has already mentioned....
2: All OnDemand & streaming apps rely on an internet connection, the TiVo's is in-built (separate from your home broadband) but this often fails without users realising. On the front-left of the box are a series of green lights, the second-from-left has a painted heart symbol next to it and is your "online" light. A static light is good, but a flashing heartbeat lights means the TiVo's internet connection has failed. Anything relying on the internet will fail when this happens.
Scenario 2 is a fault, and you should report it to Virgin Media on the usual number (150 from VM, or 0345 4541111 from any other phone). It may be an external network fault, but is often a box failure & replacement.
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